1. Field of the Invention
This invention relates to a device for automatically monitoring lengths and thicknesses of strip metal stock being fed to a metal processing machine, e.g. a power press.
2. Description of the Prior Art
A typical power press comprises a frame structure which provides a feed path for the stock between relatively movable tool-carrying members. One of the tool-carrying members is normally a ram movable rectilinearly along a guide path in a direction toward and away from the other tool-carrying members forming a bed or table on the frame structure. The driving means for the ram comprises a fly-wheel or other rotary power storage member operatively connected through a clutch with an eccentric element such as a crank, cam or eccentric serving to impart the required movement to the ram.
In the power presses, it is necessary that feed movement of the stock should be coordinated with the relative movement of the tool-carrying members so that the portion of the stock disposed at a working station between the tool-carrying members is stationary while it is engaged by and deformed or otherwise acted upon by the tools carried by the tool-carrying members. It is subjected to the necessary feed movement at such times as the tool carrying members are separated from each other by a distance sufficient to permit movement of the stock.
For efficient utilization of the stock, i.e., formation from the stock of the maximum number of work pieces, it is required that the product-forming portions of the stock should be placed as close to each other as possible. On the other hand, there are a number of variable factors such as the surface condition of the stock, surface condition of the components of the feeding device which engage with the stock to impart the necessary movement thereto and the thickness of the stock and its mechanical properties, any of which may contribute to some variation either in a random or systematic manner in the magnitude of the actual feed step imparted to the stock. These make it necessary to allow for such variation in determining the nominal value of the feed step imparted to, and hence the nominal separation between product-forming portions of the stock.
Moreover, it is often required that a particular power press shall be operated for relatively short runs of perhaps a few days or even a few hours, to produce certain products involving the application to the stock of feed movements of a certain magnitude and thereafter may be applied to the production of other products, from the same or different stock, involving feed movements of different magnitude.
The problems of controlling in an accurate manner the feeding of the stock to a power press have been largely overcome by the control unit described in U.S. Pat. No. 3,716,773 and the hydraulically powered feeder described in U.S. Pat. No. 3,771,703. However, there still remains a serious problem facing sheet metal processers today and that is the cost of the metal. This metal is typically purchased by the processer in the form of very large coils or rolls and the cost of this metal is based upon its weight. For many industries, such as the automotive industries, the metal parts formed must meet certain minimum government standards as to metal thickness or gauge. The manufacturer who produces the metal coils or rolls may encounter some difficulty in uniformity of gauge and, to be certain that all of a roll is at the minimum required gauge, he will manufacture the strip metal at a nominal gauge somewhat thicker than the required minimum. This, of course, does not hurt the metal manufacturer since he sells on the basis of weight of metal, but it does impose an additional burden on the metal processor.
Thus, the metal processer will purchase a coil of strip metal and, on the basis of its nominal thickness, he expects it to have a certain total length which will provide him with a certain number of work pieces. However, since the coils which he purchases are frequently thicker than the nominal stated thickness, the metal processer finds that the coil which he has purchased produces fewer than the expected number of work pieces. It is, of course, most difficult at this stage to prove to the metal manufacturer that the deficiency in the total number of expected work pieces was caused by the nature of the strip metal received and not by wastage on the part of the metal processer.
There is, therefore, a great need in the industry for a system which will monitor the length and thickness and determine the weight of strip metal being fed through a power press. Accordingly, it is the object of the present invention to provide a system which will give a measurement of the weight of the metal actually fed through a power press, which measurement will be acceptable both to the metal processor and the manufacturer of the coils of strip metal.